Wall Street critic troubled that instant-messaging service may be used to circumvent regulatory scrutiny

WASHINGTON—Capitol Hill’s biggest Wall Street critic is raising fresh concerns that large financial firms backing a new instant-messaging service may use it to circumvent regulatory scrutiny.

Sen. Elizabeth Warren (D., Mass) on Monday sent letters to six financial regulators saying she is troubled that the big banks and other financial firms backing Symphony Communications Services LLC may use the new tool to skirt regulatory and legal requirements, as well as escape enforcement action by the Consumer Financial Protection...